1. Field of the Invention
The invention relates to a process for preparing high-molecular-weight polyesters by reacting an aromatic dicarboxylic acid with a mixture of alkanediols and alkenediols with substantial exclusion of oxygen in the presence of a catalyst.
2. Description of the Background
High-molecular-weight polyesters are excellent materials having specific properties which enable them to be used as raw materials for strong high-tech products. It is typical of this application area that frequently, judged according to industrial criteria, relatively small amounts of polyester having an exactly prescribed high molecular weight are required.
Since, in large-scale production, polyesters are obtained continuously or batchwise in large amounts having a uniform molecular weight, it is usually uneconomical and also technically difficult to make available smaller fractional amounts having a defined high molecular weight.
Polyesters having a high molecular weight are known in the prior art. They contain, inter alia, residual amounts of unsaturated monomer components which may, if desired, be crosslinked with thermolabile compounds (DE-A 25 09 726; DE-A 25 09 790; DE-A 25 52 424). It is characteristic of these disclosures that the final molecular weight has to be set as the polyester is being synthesized. A subsequent manipulation of the molecular weight is impossible or leads to a deterioration in product properties.
In principle, it is also known in the prior art that polyesters can be subjected to a solid-phase postcondensation. However, this usually requires relatively long times. Furthermore, only a small increase in the viscosity of the polyester is achieved. A need therefore continues to exist for an effective way of preparing small amounts of polyester of high molecular weight.